Water content of flavonoid/cyclodextrin nanoparticles: Relationship with the structural descriptors of biologically active compounds

The paper presents a study regarding the obtaining, characterisation, and water evaluation of flavonoid (flavone, chrysin, naringenin, hesperetin, apigenin, fisetin, luteolin) and related compounds (cinnamic and caffeic acids, silybin)/cyclodextrin complexes. The thermogravimetric and calorimetric analyses indicate the formation of complexes, the presence of bioflavonoids and related compounds being revealed by the larger peaks from the calorimetric analysis (up to 250 °C); the dissociation of water and other volatiles (ethanol) is revealed by thermogravimetry. The Karl Fischer titration (KFT) water content of β-cyclodextrin complexes obtained by crystallisation method was in the range of 8.8% (chrysin) to 12.6% (caffeic acid), and higher for ultrasonication method (9.4–13.3%). For α-cyclodextrin complexes the water content was lower (8.2–9.8%). KFT water content correlates with the hydrophobic descriptors (i.e. octanol–water partition coefficient). This observation demonstrates the molecular encapsulation of compounds such as bioflavonoids in cyclodextrin cavity by replacing of crystallisation water molecules with the more hydrophobic guest compounds.